<?php
/**
 * 加密实现类
 */
class Xxtea {

    public static function long2str($v, $w) {
	    $len = count($v);
	    $n = ($len - 1) << 2;
	    if ($w) {
	        $m = $v[$len - 1];
	        if (($m < $n - 3) || ($m > $n)) return false;
	        $n = $m;
	    }
	    $s = array();
	    for ($i = 0; $i < $len; $i++) {
	        $s[$i] = pack("V", $v[$i]);
	    }
	    if ($w) {
	        return substr(join('', $s), 0, $n);
	    }
	    else {
	        return join('', $s);
	    }
	}

    public static function str2long($s, $w) {
	    $v = unpack("V*", $s. str_repeat("\0", (4 - strlen($s) % 4) & 3));
	    $v = array_values($v);
	    if ($w) {
	        $v[count($v)] = strlen($s);
	    }
	    return $v;
	}

    public static function int32($n) {
	    while ($n >= 2147483648) $n -= 4294967296;
	    while ($n <= -2147483649) $n += 4294967296; 
	    return (int)$n;
	}

    public static function xxtea_encrypt($str, $key) {
	    if ($str == "") {
	        return "";
	    }
	    $v = self::str2long($str, true);
	    $k = self::str2long($key, false);
	    if (count($k) < 4) {
	        for ($i = count($k); $i < 4; $i++) {
	            $k[$i] = 0;
	        }
	    }
	    $n = count($v) - 1;
	 
	    $z = $v[$n];
	    $y = $v[0];
	    $delta = 0x9E3779B9;
	    $q = floor(6 + 52 / ($n + 1));
	    $sum = 0;
	    while (0 < $q--) {
	        $sum = self::int32($sum + $delta);
	        $e = $sum >> 2 & 3;
	        for ($p = 0; $p < $n; $p++) {
	            $y = $v[$p + 1];
	            $mx = self::int32((($z >> 5 & 0x07ffffff) ^ $y << 2) + (($y >> 3 & 0x1fffffff) ^ $z << 4)) ^ self::int32(($sum ^ $y) + ($k[$p & 3 ^ $e] ^ $z));
	            $z = $v[$p] = self::int32($v[$p] + $mx);
	        }
	        $y = $v[0];
	        $mx = self::int32((($z >> 5 & 0x07ffffff) ^ $y << 2) + (($y >> 3 & 0x1fffffff) ^ $z << 4)) ^ self::int32(($sum ^ $y) + ($k[$p & 3 ^ $e] ^ $z));
	        $z = $v[$n] = self::int32($v[$n] + $mx);
	    }
	    return self::long2str($v, false);
	}

    public static function xxtea_decrypt($str, $key) {
	    if ($str == "") {
	        return "";
	    }
	    $v = self::str2long($str, false);
	    $k = self::str2long($key, false);
	    if (count($k) < 4) {
	        for ($i = count($k); $i < 4; $i++) {
	            $k[$i] = 0;
	        }
	    }
	    $n = count($v) - 1;
	 
	    $z = $v[$n];
	    $y = $v[0];
	    $delta = 0x9E3779B9;
	    $q = floor(6 + 52 / ($n + 1));
	    $sum = self::int32($q * $delta);
	    while ($sum != 0) {
	        $e = $sum >> 2 & 3;
	        for ($p = $n; $p > 0; $p--) {
	            $z = $v[$p - 1];
	            $mx = self::int32((($z >> 5 & 0x07ffffff) ^ $y << 2) + (($y >> 3 & 0x1fffffff) ^ $z << 4)) ^ self::int32(($sum ^ $y) + ($k[$p & 3 ^ $e] ^ $z));
	            $y = $v[$p] = self::int32($v[$p] - $mx);
	        }
	        $z = $v[$n];
	        $mx = self::int32((($z >> 5 & 0x07ffffff) ^ $y << 2) + (($y >> 3 & 0x1fffffff) ^ $z << 4)) ^ self::int32(($sum ^ $y) + ($k[$p & 3 ^ $e] ^ $z));
	        $y = $v[0] = self::int32($v[0] - $mx);
	        $sum = self::int32($sum - $delta);
	    }
	    return self::long2str($v, true);
	}
	
	//加密
	public static function encrypt($txt, $key = '') {
        empty($key) && $key = C('auth_key');
		$s = urlencode(base64_encode(self::xxtea_encrypt($txt, $key)));
		$s = str_replace('%2F', '%252F', $s);	// fix nginx %2F 导致 rewrite 失效的问题
		return $s;
	}
	
	//解密
    public static function decrypt($txt, $key = '') {
        empty($key) && $key = C('auth_key');
		$txt = str_replace('%252F', '%2F', $txt);	// fix nginx %2F 导致 rewrite 失效的问题
		return self::xxtea_decrypt(base64_decode(urldecode($txt)), $key);
	}

}